Processes for preparing methylchlorosilanes by reaction of silicon with chloromethane (direct synthesis) in the presence of suitable catalysts and catalyst combinations are already known. U.S. Pat. No. Re. 33,452 describes a direct synthesis process using a catalyst combination of the elements or the compounds of copper, zinc and tin. The ratio of the catalysts copper, zinc and tin to one another has a strong influence on the process, in particular on the productivity and the selectivity, while the form, such as metal, alloys or compounds, in which the catalysts are introduced into the catalyst composition, is of subordinate importance.
A. Magrini et al.; J. Phys. Chem. 93, 1989, 5563, describe the activation by means of a trichlorosilane/chloromethane mixture of surfaces of pure polycrystalline silicon on which copper has been vapor-deposited. In the subsequent reaction with pure chloromethane, a higher selectivity in respect of dimethylchlorosilane, methyldichlorosilane and methyltrichlorosilane is achieved. The proportion of dimethyldichlorosilane decreases.
U.S. Pat. No. 4,973,725 describes a direct synthesis process for selectively preparing organohalohydrosilanes in which the gas fed into the reactor comprises at least 20% by volume of hydrogen and an organohalosilane or organohalohydrosilane as activator.